Pressure is increasing on international and especially American power producers to curtail or limit the production of gases that contribute to global warming. Of particular interest amongst these gases are carbon monoxide and carbon dioxide, which are produced by the burning of fossil fuels. At the same time, the seemingly unrelated environmental harm of enormous waste production by the most highly developed nations continues to accrue. This waste accumulates when, at the end of their useful life or even during their manufacture, objects made of materials containing carbon-hydrogen bonds become waste. As this waste is generated at diverse locations often far removed from a location optimal for recycle or reuse, these materials end up in landfill waste or decompose in the natural environment.
Examples of such materials include cellulosic materials such as paper, wood, sawdust, bark, cotton and plant waste such as bagasse; thermoplastic materials such as polyethylene, polypropylene, poly vinyl, polyester, styrene and nylon; the thermosetting plastics such as formaldehyde, rigid urethane and foamed urethane; elastomers such as rubber, neoprene and butadiene rubber. All of these materials may be found in the automobile. When autos end their useful life they are commonly shredded and the bulk of metals are recovered and recycled. The remainder of the auto reports to a fraction called “fluff” consisting of unrecovered metals, paper, wood, rubber, plastics, foams, cloths, textiles, circuit boards and large amounts of insulated copper wire. More than four million tons of fluff is generated yearly in the United States alone, with the vast majority being landfilled at great cost and environmental disadvantage. Rubber tires also represent an environmental problem. Similar to fluff, shredded tires contain the residue of steel belts and zinc oxide and sulfur as contaminants.
Attempts have been made to recover value from fluff. These attempts involved various techniques to separate some of the individual plastics which might have sufficient value to justify the expense of separation. In general the non-homogeneity of the feed, and the large weight of undesirables, have discouraged these efforts as it is difficult to extract a clean single material from this mass of soiled material.
In forest management and in the production of wood products, large quantities of “slash” sawdust, and bark are created. In agriculture, chaff such as bagasse is generated. The burning of these materials is energy inefficient and polluting to the atmosphere. Conversion to valuable and readily transported carbon will be very advantageous.
In the preparation of solid fuels such as coal, substantial losses of coal occur in meeting current quality standards requiring the removal of impurities such as sulfur, nitrogen complexes, and heavy metals. Reacting the carbon-hydrogen bond portions of coal produces a carbon product from which impurities are more easily removed.
The problem of waste organics has long been recognized and many attempts to solve it have been made. These solutions have been primarily directed to pyrolysis of the material in an attempt to recover useful hydrocarbon products. Given the complex nature and variability of the waste feeds, this is an almost impossible task.
U.S. Pat. No. 4,166,786 to Duraiswany teaches a process to pyrolyze coal to produce liquid hydrocarbons. The process uses carbon dioxide as a “transfer gas” at temperatures of 1400° F.-1800° F. (760° C.-986° C.). At these temperatures the carbon dioxide will react with carbon to form carbon monoxide, but will not react with carbon-hydrogen bonds to produce carbon. Similarly, U.S. Pat. No. 5,853,687 to Morlec teaches the conversion of waste rubber to carbon black at high temperatures. The resulting pyrolysis hydrocarbons are burned to provide heat for the reaction. Carbon dioxide is used as an “inert” gas for carrying the hydrocarbons.
U.S. Pat. No. 5,470,380 to Cha teaches a two stage process that produces light oils as the product. U.S. Pat. No. 6,548,197 to Chandron uses a combination of high temperature and the water gas reaction to provide added hydrogen for the production of hydrocarbons.
U.S. Pat. No. 3,843,457 to Grannen uses the microwave at low temperatures (200° C.) to process waste organics into a mixture of organic acids, aldehydes, ketones and alcohols. Similarly U.S. Pat. No. 5,084,140 to Holland discloses the use of microwave energy and inert atmospheres to pyrolyze at high temperatures (at least 800° C.), producing a mixture of hydrocarbons.
U.S. Pat. No. 5,084,140 to Chandron teaches a method of converting biomass and other carbonaceous feeds into a hydrogen-rich medium BTU fuel gas for use in a fuel cell. The method uses a fluid bed of various materials including magnesium oxide, alkali carbonates and carbon to effect its results. The process involves providing heat from combustion of part of the product it produces for the steam reforming endothermic reactions which include the water gas reaction to convert carbon to hydrogen and carbon monoxide. The reaction operates at very high temperatures and consumes carbon rather than producing it. Additionally, the reaction requires a novel heat exchange method to overcome the strongly endothermic pyrolytic reaction.
The basic difficulty with these various pyrolysis techniques is that they result in a complex mixture of hydrocarbon products which require a petroleum refinery-like facility to produce marketable end products. Thus, there is a need for a process that can accept a very wide variety of feedstocks and produces a single carbon product, namely carbon, that can be used for energy production. Preferably, this would be an exothermic process such that energy is gained in producing the carbon and limiting the environmental consequences associated with this waste.